The present invention relates to a method for assembling the plates of a plate pack for a heat exchanger and resulting plate pack.
In general, plate packs for a heat exchanger comprise a stack of plates parallel to each other.
The plates, consisting of thin sheet metal, most often made of stainless steel or any other suitable material, comprise borders with a smooth surface and a central heat-exchange part which is usually provided with corrugations by means of which they are in contact with each other and by means of which they define the circuits for flow of at least two independent fluids.
The flow of the fluids between the plates may be of the co-current, counter-current or crossflow type and each circuit is connected to collectors for intake and return of fluids.
Usually, the plates are assembled two by two using connection tabs welded to the borders with a smooth surface in order to form plate pairs and these plate pairs are superposed and assembled together so as to form the plate pack.
The connection tabs are placed at particular locations in order to define inflow and outflow regions allowing the flow of said fluids between the plates.
Hitherto, the plates of each plate pair were assembled as follows.
First of all, at least one tab is positioned at particular locations on the lower face of the borders of the upper plate, then said tab is connected by welding to said plate in order to form a first subassembly.
Next, at least one tab is positioned at particular locations on the upper face of the borders of the lower plate, then said tab is connected by welding to said plate in order to form a second subassembly.
Each weld bead is made along the edge, that is to say that it covers the free ends of the corresponding plate and of the tabs.
Next, the two subassemblies are superposed and held pressed one on the other for example by means of a press. These two subassemblies are connected together by a third weld bead made along the edge, that is to say that it covers the two previous weld beads connecting the plate and the tabs of each subassembly.
The plate pairs thus produced are superposed and a layer of welding is deposited over the entire height of each lateral surface of the plate pack in order to form a wall of sealed weld.
However, this method of assembly has drawbacks.
This is because it requires special tooling and many steps in order to assemble all the plates.
Furthermore, at the time of superposing the plate pairs, alignment defects may occur which create interstices forming sites susceptible to corrosion.
To avoid these defects, another method consists in forming, on the border to be connected of each plate to the adjacent plate, a flange folded at 90xc2x0 with respect to the central part of the corresponding plate, in superposing the plates by applying the free ends of the flanges one on the other and in making a weld bead over each mating plane with or without filler metal.
However, this assembly method also has drawbacks, the main one of which lies in the fact that bringing the various plates into contact with each other is awkward, given the small thickness of these plates, so that the welding operation is also difficult to carry out.
Furthermore, the weld bead may have defects which may impair the seal of the plate pack given the pressures prevailing inside the circuit.
The subject of the invention is therefore a method for assembling the plates of a plate pack for a heat exchanger formed by a stack of plates together defining at least two flow circuits for independent fluids and each comprising a central heat-exchange part and borders with a smooth surface, characterized in that:
a cutout is produced on the corners of each plate,
on the border to be connected of each plate to the adjacent plate, a fold is made in order to form a first flange,
on this first flange, a fold is made in order to form a second flange lying parallel to the central part of the corresponding plate and directed outward from said plate,
the plates are superposed and held by applying the second flange of each plate to the second flange of the adjacent plate, and
a continuous sealed weld bead is made by melting the second superposed flanges of adjacent plates.
According to other characteristics of the invention:
the weld bead is made by complete melting of the second superposed flanges of adjacent plates,
a closure plate is placed on the upper part and on the lower part, respectively, of the plate stack, and each closure plate is welded by a continuous sealed weld bead to the flange of the adjacent plate
each side face of the plate stack is partially closed by a covering plate.
the second flange forms, with the first flange, an angle equal to or different from the angle formed between the first flange and the central part of the corresponding plate and each angle is, for example, between 75 and 105xc2x0.
The subject of the invention is also a plate pack for a heat exchanger, characterized in that it comprises plates superposed and assembled by the aforementioned method.
According to other characteristics of the invention:
each plate has the shape of a quadrilateral comprising a central heat-exchange part and four borders with a smooth surface, each one fitted with a folded flange, the four folded flanges being directed alternately upward and downward,
the plate pack comprises a closure plate placed on the upper part and on the lower part, respectively, of the plate stack, each closure plate being connected to the flange of the adjacent plate by a continuous sealed weld bead,
the plate pack comprises a covering plate placed on each side face of the plate stack partially closing the corresponding side face.